Fundamental Physics Over 27 Orders of Magnitude With Pulsars

Ryan LynchGreen Bank Observatory

Image Credit: ESO

Physics Frontiers Center

Pulsars are clocks...

...that create some of the most extreme environments in the

Universe...

...which makes them natural laboratories for studying fundamental

physics

Pulsar Timing

● Track every rotation of a pulsar

● Predict pulse arrival times– Deviations from the expected arrival time of a pulse

contain useful information

Time

Model (Prediction)

Time

Model (Prediction)

Data (No Noise)

Time

Resid

ual

Model (Prediction)

Data (No Noise)

Residual = Data ­ Model

Times of Arrival (TOAs)

Many rotations

Resid

ual

Time (weeks to years)

Residual = Data ­ Model

Data (With Noise)

Model (Prediction)

Power of Pulsar Timing

● Spin period can be measured to ~d/Nrot

– For MSPs observed over many years, Nrot~109

● At 2017-10-17 09:10 EDT the frequency of PSR J0437-4715 is/was

173.701580684374 ±

0.000000000003 Hz

a = 1011 cm (1.44 Rsun)a-b = 18.59 ± 0.01 cm

Orbit at D = 139 pcmeasured to 10-13!!!

Power of Pulsar Timing

Effects of the Interstellar Medium

● Two frequency-dependent effects: dispersion and scattering

● Both smear out pulses and are worse at low frequencies

● They are also timing varying!

20 June 2013 IPTA Krabi

=

W h i t e n o i s e r e s i d u a l s

R a d i o m e t e r n o i s e P u l s e J i t t e r D I S S

Slide courtesy of Tim Dolch

20 June 2013 IPTA Krabi

=

R e d n o i s e r e s i d u a l s

f − 5

S p i n n o i s e +f − 8 / 3

D M v a r i a t i o n s +f − 1 3 / 3

G W s ( s t o c h a s t i c )

5 3 0 0 0 5 3 5 0 0 5 4 0 0 0 5 4 5 0 0 5 5 0 0 0 5 5 5 0 0 5 6 0 0 0 5 6 5 0 0M J D

0 . 0 0 0

0 . 0 0 1

0 . 0 0 2

0 . 0 0 3

0 . 0 0 4

∆D

M(t

)(p

ccm

−3 )

B 1 9 3 7 + 2 1 D M V a r i a t i o n s N A N O G r a v O b s e r v a t i o n s

1 0 0 1 0 1 1 0 2 1 0 3

L a g ( d a y s )

1 0 − 8

1 0 − 7

1 0 − 6

1 0 − 5

DD

M(τ

)(p

ccm

−3 )2

B i n n e d S t r u c t u r e F u n c t i o n

Slide courtesy of Tim Dolch

Millisecond Pulsar Timing Arrays

● GWs will cause a quadirpolar angular correlation signature

● Requirements: 10-100s ns residuals, full sky coverage, lots of pulsars, precise ISM measurements

Image credit: NANOGrav

The Hellings­Downs Curve

Image credit: David Champion

GW Sources

● Coalescing Super-Massive Black Holes– Basically all galaxies have them– Masses of 106 – 109 M⊙– Galaxy mergers lead to BH mergers– When BHs within 1pc, GWs are main energy

loss– For total mass M/(1+z), distance dL, and SMBH

orbital freq f, the induced timing residuals are:

– Cosmic strings (if they exist) also in this GW frequency range

Slide courtesy S. Ransom

Observational Signatures

● Different source classes have different structure in residuals

● Sensitive to fGW ~ nHz / λGW ~ 1017 m

Image credits: NANOGrav

Complementary Gravitational Wave Detectors

“High RiskHigh Reward”

Moderate RiskHigh Reward

NANOGrav

● North American PTA

– Senior/affiliated researchers at over two dozen institutions (US, Canada, Europe)

● Funded by NSF Physics Frontier Center ($14.5M over 5 years)

– Portion of funding supports GBT operations

● Currently time 45 pulsars at GBT and Arecibo

– 500 (GBT) + 800 (AO) = 1300 hrs/year

– Does not include pulsar searches!

– Each contributes 50% of overall GW sensitivity

● International collaboration through IPTA

Physics Frontiers Center

NANOGrav Data Releases

5 Year (2013)

– ASP + GASP

– 16 MSPs, 1,095 observations, ~16K TOAs

9 Year (2015)

– Transitioned to [GP]UPPI

– 39 MSPs, 4,138 observations, ~170K TOAs

11 Year (2017)

– 45 MSPs, 6,737 observations, ~310K TOAs

“Current” Results

Arzoumanian et al. (2016)

● Ruling out/tightly constraining early models of BH merger rate

● Constraints on shape of GW spectrum contains information about BH environments

Physics Frontiers Center

Demorest et al. 2010, Nature, 467, 1081D

Most highly cited GBT paper (1,550+)

Mwd

= 0.500(6) M⊙M

psr = 1.97(4) M !⊙

Inclination = 89.17(2) deg!

Full Shapiro Signal

No General Relativity

Full Relativistic Solution

Amplitude ∝ Comp. MassNarrowness ∝ Inclination

Conjunction

Subatomic Physics

Subatomic Physics

Rules out most or all EOSswith exotic material in the cores

Strong Field GR Tests

● Double Pulsar is the premier system for studying strong-field GR

– Light from one pulsars passes within 10,000 km of the other

● Seeing 2nd order post-Newtonian effects

Courtesy of Michael Kramer

Testing the Strong Equivalence Principle

Image credit: Ransom et al. (2014, Nature, 505, 520)

● PSR J0337+1717: First MSP in a stellar triple system

– Discovered in GBT survey

● Three body dynamical effects cause secular changes in orbital parameters

– Allow us to precisely solve for the geometry and masses of all stars and orbits

● All bodies fall at the same rate (?)

● MSP & inner WD falling in gravity of outer WD

Testing the Strong Equivalence Principle● Violations parameterized by differential

acceleration

Currently dominated by systematics

Sensitive to Solar wind DM variations

Current best limit on differential acceleration Δ = 10-6

100x improvement over Lunar ranging tests

Look for Archibald et al. (early 2018)

Testing TeVeS Gravity Theories

● J0348+0432: Relativistic MSP/WD binary

– Discovered by GBT

● Pulsar + WD spectroscopy → double-line binary

● Get masses + system geometry

● Pulsar is 2 Msun – most massive known (by a hair)

– Does not significantly improve on EOS constraints

● But…

Antoniadis et al. (2013, Science, 340, 448)

Testing TeVeS Gravity Theories

● Relativistic orbit and mass asymmetry provide unique test of tensor-vector-scalar gravity theories

– Differeing “compactness” would produce dipolar GWs

● Significant parameter space for scalar coupling constants ruled out thanks to high binding energy and relativistic orbit

Antoniadis et al. (2014, Science, 340, 448)

Where Are We Going?

~0.6-4 GHz in one shot CASPER-based backend Improve timing by 20-100%

Bandwidth: - Improves S/N (as √(BW)) - Scintillation protection - Much better ISM (i.e. DM) removal

ASP / GASP GUPPI / PUPPI Wideband

Fig: Paul Demorest

Where Are We Going?

● Daily observations of all NANOGrav MSPs w/ CHIME

– All pulsars with ~ few weeks cadence

● Large FOV

● No moving parts – digital telescope

● Relatively inexpensive way to get collecting area

Where Are We Going?

● Stochastic GW background detected by 2022

– Assumes steady growth in current observing program

● Not just a number!

– Spectral shape encodes information about supermassive BH environments

– Find the solution to the last parsec problem

● Detect single GW sources?

● Burst events?

– Bursts with memory provide deep test of GR

● Constrain (detect?) cosmic strings

● Eventually measure anisotropies in GW background

Where Are We Going?

● More pulsars! Always more pulsars!

– Every time we find new pulsars, we find true gems

– Take advantage of new capabilities (PAFs, UWB Rx)

● Next generation surveys (FAST, MeerKAT, SKA) will find many thousands of new pulsars

– Eventually all the pulsars

● 3 Msun neutron stars? Sub-millisecond pulsars?

– Solve the NS EOS?

● Pulsar – BH binary? (“Holy Grail” for gravity tests), Pulsars around Sgr A*

– Test no-hair theorem

– Maybe, finally, find breakdown of GR?

Summary

● NANOGrav is on track to detect GWs in the next 5 years– Opening the full GW spectrum

● We are on the cusp of a new wave of pulsar discoveries– There will undoubtedly be unique and powerful physical

laboratories among them

● The GBT (and Arecibo) are the best instruments in the world for precision pulsar timing– Wideband systems could make them even better– Can leverage new telescopes to maximize scientific return